AB0795 MPO-ANCA ANTIBODIES: ASSOCIATED DISEASES, SPECIFICTY, AND RELATION WITH SEVERITY AND PROGNOSIS OF UNDERLYING VASCULITIS. STUDY FROM A SINGLE UNIVERSITY HOSPITAL
Authors: S. Al Fazazi, V. Calvo-Río, M. Renuncio García, M. Rodriguez Vidriales, C. Escagedo Cagigas, J. Irure-Ventura, L. Martín-Penagos, M. Lopez-Hoyos, R. Blanco
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitis (AAV) include Granulomatosis with polyangiitis GPA), Microscopic polyangiitis (MPA), and Eosinophilic granulomatosis with polyangiitis (EGPA). Anti-myeloperoxidase (anti-MPO) or anti-proteinase 3 are the two main ANCA subtypes. Anti MPO specificity and correlation with the severity and prognosis of underlying vasculitis is contradictory <b>[1].</b> <h3>Objectives</h3> To assess, in patients with positive anti-MPO, <b>a</b>) associated diseases, <b>b</b>) specificity in diagnosing AAV and, <b>c</b>) relation with severity and prognosis of underlying vasculitis in a single university hospital. <h3>Methods</h3> Study of patients with positive anti-MPO from a University Hospital, from 2003 to 2022. ANCA was determined by standard inmunohistochemistry. The specificity of anti-MPO for diagnosis and relation with severity and prognosis of underlying vasculitis were evaluated with Receiver Operating Characteristics (ROC) curves. At diagnosis severe AAV were considered cases with renal disease (hematuria and/or proteinuria) and pulmonary involvement. In follow-up, worst prognosis was considered if the patient needed dialysis, a transplant or died. <h3>Results</h3> We study 101 patients with positive anti-MPO. <b>Table</b> summarizes the prevalence of these antibodies in vasculitis and non-vasculitis diseases. Most of them (76.23%) had an underlying AAV, being the most frequent MPA (33.7%). The non-vasculitis disease more frequent was neoplasm (4,9%). For anti-MPO antibodies with a diagnosis of AAV (n=77), an area under the curve (AUC) was calculated (AUC=0.8084), and a cut-off point of 41.5 IU/ml was determined (<b>Figure</b>). When the analysis was restricted to exclusively MPA (n=34), the cut-off point was 36.5 IU/ml with an AUC of 0.6435. For severity of AAV, there were significant differences in anti-MPO levels between patients with renal or pulmonary dysfunction (n=65) versus those without them (n=36) (p=0.0003), and a cut-off threshold of 60 IU/ml was established. Finally, after evaluating the illness's prognosis, an AUC= 0.5546 was found, being no significant differences between those patients who had a worse disease progression (n=19) and those who did not (n=82) (p=0.4643). <h3>Conclusion</h3> MPO antibodies levels, at the moment of diagnosis, may be associated to AAV diagnosis (specificity) and severity but not with disease outcome. <h3>References</h3> [1]Walker BS, et al. Autoimmun Rev. 2022 Jun;21(6):103100. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Salma Al Fazazi: None declared, Vanesa Calvo-Río: None declared, Mónica Renuncio García: None declared, Maria Rodriguez Vidriales: None declared, Clara Escagedo Cagigas: None declared, Juan Irure-Ventura: None declared, Luis Martín-Penagos: None declared, Marcos Lopez-Hoyos: None declared, Ricardo Blanco Speakers bureau: Abbvie, Pfizer, Roche, Lilly, Bristol-Myers, Janssen, Galapagos, MSD, Consultant of: Abbvie, Pfizer, Roche Lilly, Bristol-Myers, Janssen, MSD, Grant/research support from: Abbvie, MSD, Novartis, Roche.